Embodiments of the invention relate generally to an isolation and feedback system for an electrical energy storage system that, in one embodiment, is applicable to electric drive systems including hybrid and electric vehicles.
Hybrid electric vehicles may combine an internal combustion engine and an electric motor powered by an energy storage device, such as a traction battery, to propel the vehicle. Such a combination may increase overall fuel efficiency by enabling the combustion engine and the electric motor to each operate in respective ranges of increased efficiency. Electric motors, for example, may be efficient at accelerating from a standing start, while internal combustion engines (ICEs) may be efficient during sustained periods of constant engine operation, such as in highway driving. Having an electric motor to boost initial acceleration allows combustion engines in hybrid vehicles to be smaller and more fuel efficient.
A purely electric vehicle (EV) uses stored electrical energy to power an electric motor, which propels the vehicle and may also operate auxiliary drives. Purely electric vehicles may use one or more sources of stored electrical energy. For example, a first source of stored electrical energy may be used to provide longer-lasting energy (such as a low-voltage battery) while a second source of stored electrical energy may be used to provide higher-power energy for, for example, acceleration (such as a high-voltage battery or an ultracapacitor).
Plug-in electric vehicles (PHEV), whether of the hybrid electric type or of the purely electric type, are configured to use electrical energy from an external source to recharge the energy storage devices. Such vehicles may include on-road and off-road vehicles, golf carts, neighborhood electric vehicles, forklifts, and utility trucks as examples. These vehicles may use either off-board stationary battery chargers, on-board battery chargers, or a combination of off-board stationary battery chargers and on-board battery chargers to transfer electrical energy from a utility grid or renewable energy source to the vehicle's on-board traction battery. Plug-in vehicles may include circuitry and connections to facilitate the recharging of the traction battery from the utility grid or other external source, for example.
Thus, hybrids and EVs in general typically include at least one, and oftentimes several, low or high voltage storage devices or other sources of power. Known devices include but are not limited to a power battery that operates at 400 V or greater, an energy battery operating optimally at 120 V, or an auxiliary power unit (APU) that may include an internal combustion engine (ICE), a permanent magnet generator (PMG), or a fuel cell (FC). The APUs for use in an electric vehicle may have their own unique operating voltage which may be at 400 V or greater as well. For instance, at a desired operating condition an ICE may output a voltage that is different from that of, for instance, a power battery or from other operating voltages of high voltage devices in an EV. Or, a PMG may itself operate at an operating voltage that is different from other devices within a system. Further, EVs often include high voltage devices that vary from manufacturer to manufacturer and from one type to another. For instance, one manufacturer may fabricate an ICE that outputs optimally 400 V while another manufacturer may fabricate an ICE that outputs 380 V optimally. As such, components and sub-systems may be designed into a hybrid or an EV having a wide variety of operating voltages.
During the design cycle of a hybrid or an EV, it is often desirable to be able to swap out different high voltage sub-systems in order to test the sub-system for eventual inclusion in the final design. That is, APUs that include ICEs, PMGs, or FCs may be tested and swapped out with other devices any number of times before settling on the final unit(s) to be used. Similarly, different high voltage power batteries and relatively low voltage energy batteries may likewise be tested during a lengthy and rigorous design and testing stage. As is known in the art, it is desirable to enable simple and quick connection and disconnection of such sub-systems during the design and test stage (i.e., during the experimental stage) of a hybrid vehicle or EV. Oftentimes the connection/disconnection functionality is provided by use of electro-mechanical contactors that are all controlled by a main processing unit.
Electro-mechanical contactors are used in a variety of environments for turning on and off a power source to a load electrically. The contactors include movable contacts and fixed contacts. The movable contacts are connected to an electromagnet and are controlled to selectively turn on or off power from the source to the load. The contacts are typically maintained in an open position by way of a spring and are caused to translate to a closed position when power to the electromagnet's coil is applied.
The contactors for high voltage operation typically include specific design parameters in order to provide the necessary operation capability. In systems where high voltage energy storage devices are being used, contactors are often included for safety purposes. It is often desirable for safety purposes to monitor voltages and currents in order to provide quick and safe shutdown in the event of a voltage or current excursion. In order to provide the safety features in early experimental hybrid and EV designs, it is therefore often necessary to provide supporting hardware to operate the contactors and monitor the currents and voltages particular to each voltage device. Thus, one set of contactors and supporting hardware may have hardware and control settings specific to a 400 V operation of a power battery, another set of contactors and supporting hardware may have control settings specific to a 120 V operation of an energy battery, and another set of contactors may be specific to a voltage of an auxiliary power unit. Subsequently, when it is desired to continue testing of the design by swapping out components, the 400 V power battery may be changed out for another power battery having a different operating voltage, or perhaps for a different energy storage device type altogether (such as, for instance, an ultracapacitor).
Because each device being tested may have unique performance capability and/or operating voltage, when components are swapped the contactors or their control settings may prove to be inadequate, as well as the additional hardware used to provide current and voltage monitoring. As such, each swap of a hardware component can result also in a need to swap out the contactors, to swap out the current and voltage monitoring, and/or to alter the control parameters for contactor operation.
When preparing a test setup of a hybrid or an EV, it is often necessary to include hardware connections and feedback monitoring capability of the specific devices being tested. That is, each device (storage, APU, etc. . . . ) typically includes its own contactors and feedback system that is specific to the device being tested. Thus, whenever re-arranging components, swapping out components, or adding new components, additional contactors and feedback monitoring capability is also included in order to provide the necessary functionality specific to each component. Because this functionality may be so specific, a significant amount of additional work is necessary when changing out components. That is, control schemes (overall current, rate of current change, contactor voltage, etc. . . . ) may change based on the type of component being used. Because the control scheme for testing the unit is typically implemented in a main control unit, changing out components can result in a need to make costly and time-consuming changes to both hardware and software control schemes.
In fact, more generally, when testing experimental systems having multiple energy storage and supply devices therein, such problems are also encountered as well. That is, in general when experimental systems are being tested in order to determine optimal system performance, and when such systems include potentially multiple different types of energy storage and supply systems, often the experimental stage is hindered because of the costly and time-consuming need to monitor and provide feedback from the sub-systems being tested. Such systems may include but are not limited to trains, aircraft, ships, wind-power systems, solar photovoltaic systems, to name but a few. Thus, the problem is not limited to hybrid vehicles or EVs, but includes any system that may require complex experimental systems having multiple energy storage and generating sub-systems associated therewith.
It would therefore be desirable to provide a contactor that is independently controllable without a need to change out hardware and control schemes when swapping out devices in a system having one or more devices that are selectively isolated.